The present invention relates to an electrophotographic copying machine and, more particularly, to a device for detecting the size of a copy document on a document table for an electrophotographic copying machine.
An electrophotographic copying machine produces an electrostatic latent image on an optical-sensitive member. The latent image corresponds to an image on a copy document such as a manuscript or book to be copied. Toner particles are electrically adhered to the latent image, so that the latent image becomes visible to form a toner image.
The toner image is transferred onto a copy paper via a transference charger. Depending upon the size of the copy document, the size of the copy paper should be selected. To properly select the copy paper size, some sensors must be provided adjacent the document table for detecting the size of the copy document.
Conventionally, pairs of document size detecting elements are provided each of which comprises a light emitting element and a light receiving element. The number of said size detecting elements correspond to the number of the kinds of copy papers, and the sizes of the papers to be detected. The light emitting element is positioned on the document cover which is pivotably mounted on the document table. The light receiving element is positioned beneath a document table plate. When a specific size copy document is positioned on the document table and the document cover is closed to cover the copy document on the document table plate, the copy document interrupts light from the light emitting element to the light. By detecting the light receiving element which is not received by the light receiving element, the specific size of the copy document can be detected.
In the above conventional device, it is difficult to detect the specific size of the copy document when the copy document is fairly transparent, so that the S/N ratio of the light receiving element is too poor to correctly detect the particular size of the copy document. Further, the light emitting element or the light receiving element must be positioned on the document cover, so that careful consideration must be taken for problems in wiring the element at the document cover which must be pivotably activated. The document cover must be closed to cover the copy document on the document table.
Otherwise, both the light emitting element and the light receiving element are positioned beneath the document table. When a specific size copy document is positioned on the document table plate, light from the light emitting element is reflected by the document, and the reflected light is received by the light receiving element, so that the specific size of the copy document can be detected. In this device, neither the light emitting element nor the light receiving element is positioned on the document cover, so that the problems in wiring the element at the document cover which must be pivotably activated, can be solved. Further, the size of the copy document can be detected when the document cover is opened.
However, because the light receiving element receives the light reflected by the copy document, in case where the document cover coveres the copy document on the document table plate, it may be difficult to decipher the copy document from the copy document cover and, further, the presence of the dark color copy document cannot be detected, so that erroneous detection of the size of the copy document cannot be avoided.